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OVERVIEW OF DIGITAL IMAGING AND RADIATION PROTECTION ISSUES

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[From: Handbook of Medical Imaging, Volume I., Chapter 4, J. Beutel et al, eds, SPIE ... High patient radiation exposure vs conventional screen/film radiography ... – PowerPoint PPT presentation

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Title: OVERVIEW OF DIGITAL IMAGING AND RADIATION PROTECTION ISSUES


1
OVERVIEW OF DIGITAL IMAGING AND RADIATION
PROTECTION ISSUES
  • Robert M. Gagne
  • MICAB/DECS/OST
  • rmg_at_cdrh.fda.gov

From Handbook of Medical Imaging, Volume I.,
Chapter 4, J. Beutel et al, eds, SPIE Press 2000
2
What is the purpose of this presentation?
  • Here are a couple reasons
  • interest in digital imaging!
  • some concerns related to radiation safety and
    effectiveness
  • potential for exposure increase (and/or
    reduction??)
  • Forces a re-visit of some actions in the far
    radiological health past
  • imaging system inefficiency
  • Review of options (regulatory or otherwise) for
    dealing with actual and/or perceived concerns

3
What kind of equipment?
  • Digital radiography (DR)
  • not digital fluoroscopy using CCD cameras
  • not film digitizers
  • Three different types of DR systems
  • flat panel imaging arrays
  • computed radiography systems
  • CCD based - optically coupled systems

What are the concerns?
  • No equivalence to "speed" or self limitation as
    in screen/film systems
  • Inefficient" systems possible?

4
Flat Panel Imaging Arrays(indirect conversion)
From Medical Imaging, 2000
Image Formation
From Handbook of Medical Imaging, Volume I.,
Chapter 4, J. Beutel et al, eds, SPIE Press 2000
5
Flat Panel Imaging Arrays(direct conversion)
From Medical Imaging, 2000
Image Formation
From Handbook of Medical Imaging, Volume I.,
Chapter 4, J. Beutel et al, eds, SPIE Press 2000
6
Flat Panel Imaging Arrays
Number of Pixel Elements (3000 x 2500)
From Handbook of Medical Imaging, Volume I.,
Chapter 4, J. Beutel et al, eds, SPIE Press 2000
Pixel Element Size ( 0.14 mm x 0.14 mm )
From Handbook of Medical Imaging, Volume I.,
Chapter 4, J. Beutel et al, eds, SPIE Press 2000
7
Computed Radiography
Image Formation
From Handbook of Medical Imaging, Volume I.,
Chapter 5, M. Yaffee, eds, SPIE Press 2000
Pixel Elements ( 0.2 mm x 0.2 mm )
Pixel Elements (2160 x 1800)
8
CCD based - lens coupled DR system
From P. Sund et al, Proc. SPIE 3977 437 2000
CCD based - fiber optic coupled DR system
From Handbook of Medical Imaging, Volume I.,
Chapter 4, J. Beutel et al, eds, SPIE Press 2000
Pixel Elements (3000 x 2500)
Pixel Element ( 0.14 mm x 0.14 mm )
9
What are radiation protection and safety issues?
  • Unique characteristics of screen/film imaging
    systems
  • self limitation of patient exposure
  • concept of "speed" defined and understood
  • New considerations for digital radiography
  • no self limitation as in screen/film systems
  • no consensus on speed
  • "inefficient" systems possible?

10
Film/Screen Self Limitation
  • Imaging task with large dynamic range
  • Be careful not to under or over expose film
  • Self limitation of patient exposure

11
Film/Screen Speed
Difference in speed of about 2
  • Film/screen speed
  • speed 100/E where E is exposure in mR to
    produce an optical density of 1.0
  • position on exposure axis dependent on speed
  • higher speed number translates to lower patient
    exposure

12
DR Speed
  • DR operating point
  • equivalence to film/screen speed set at
    installation?
  • no self limitation except at extreme ends of
    the gray-scale transfer curve
  • patient exposure increase / decrease /
    equivalence compared to film/screen?

13
Imaging System Inefficiency
  • Chest radiography - screening program (60s-70s)
    for cardiopulmonary disease
  • need for rapid, economical imaging system
  • Photofluorographic (PFG) imaging system
  • mobile vans

14
Public Health Concerns
  • Low detection rate for tuberculosis, heart
    disease, and other respiratory diseases
  • High patient radiation exposure vs conventional
    screen/film radiography
  • BRH develops standard technique for estimating
    patient exposure

15
Digital Radiography (CCD based - lens coupled)
  • Careful system design to overcome inefficiencies

16
Level of Public Health Concern
From Medical Imaging, 2000
  • Installation base is small (even smaller for CCD
    based - lens coupled systems)
  • computed radiography not included
  • Basic questions Is there evidence of higher
    patient radiation exposure with these imaging
    systems screen/film radiography?

17
Options
  • Tracking exposure levels
  • NEXT 2001 chest radiography
  • diagnostic reference levels (ICRP, AAPM, many
    others)
  • practical tools for managing radiation dose
    levels to patients
  • Quality assurance programs
  • Performance evaluation of Computed radiography
    system, Med. Phys. 28(3), March 2001
  • Diagnostic x-ray Performance Standard
  • performance requirements on levels of imaging
    performance such as detective quantum efficiency
    (DQE)
  • dose display at operators console

18
Dose Display
  • Previous slide describes several viable options
  • TEPRSSC radiation standards and safety
    committee
  • Diagnostic x-ray Performance Standard
  • dose display at operators console for all
    radiographic equipment
  • Practical considerations yet to be explored or
    evaluated
  • cost
  • effectiveness
  • alternatives?
  • dose descriptor and definition?
  • tie to diagnostic reference levels
  • effective resource allocation

19
Summary
  • Different types of DR
  • flat panel imaging arrays
  • computed radiography systems
  • CCD based - optically coupled systems
  • Radiation safety and effectiveness issues
  • no equivalence to "speed" as in screen/film
    systems
  • "inefficient" systems
  • present revisits the past
  • potential for exposure reduction and/or
    increase??
  • Options for dealing with perceived and/or actual
    concerns
  • one suggested regulatory approach
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